You can boot Wii Menu and then go to File => Change disc to load your ISO, but right now Wii games doesn't seem to be able to save if you boot the game from Wii Menu (or even doesn't load), and for any GC ISO you'll get "unknow disc" message. About Riivolution I'm not 100% sure, but I think not...

Booting from the wii menu used to work, but it was broken when an accuracy improvement (I forget what it was) was made to the emulator. They weren't able to make those two changes play nice, so the devs had to choose between wii menu booting or the accuracy improvement. They went with the accuracy improvement. It will probably be fixed later.

You can boot, but almost every game I tried keep complaining about not finding the save file (even if you have a save file), and trying to create a new file triggered "Wii system memory is full" errors. What I've noted is that when you boot a Wii game through Wii menu, it tries to load/create save data form inside the Wii Menu Folder (User\Wii\Title\00000000\00000001), and because of that, it fails...